The usage of multiple antennas at both ends of the wireless link has been shown to provide significant capacity gains in fading environments, G. J. Foschini and M. J. Gans, On Limits of Wireless Communications in a Fading Environment when Using Multiple Antennas, Wireless Personal Communications, 6:311-335, 1998 and E. Teletar, Capacity of Multi-antenna Gaussian Channels, European Transactions on Telecommunications (ETT), 10(6), November/December 1999.
A variety of multiple-input multiple-output MIMO schemes including space-time codes and spatial multiplexing have been proposed in order to exploit those capacities. However, most multiple-input multiple-output MIMO techniques require knowledge of the channel coefficients at the receiver, which knowledge may be obtained from a channel estimation. However, channel estimation is a more sever problem in multiple-input multiple-output MIMO systems than in single antenna systems since more subchannels have to be estimated and the energy of pilot symbols has to be distributed over several October 2002.
Further, differential transmit diversity with multiple amplitude levels was proposed in X.-G. Xia, Differential En/Decoded Orthogonal Space-Time Block Codes with A PSK Signals, IEEE Communications Letters, 6(4):150-152, April 2002, and uses DAPSK signals as proposed in H. Rohling and V. Engels, Differential Amplitude Phase Shift Keying (DAPSK)—A New Modulation method for DTVB, International Broadcasting Convention, pp. 102-108, 1995 as input for a unitary space-time modulator according to B. Hochwald and W. Swelden, Differential Unitary Space-Time Modulation, IEEE Transactions on Communications, 48(12):2041-2052. Here, an outer forward error correction FEC coding is not considered.
Further, in D2, Tonello A. M “Performance of Space-Time Bit-Interleaved Codes in Fading Channels with Simplified Iterative Decoding”. Here, decoding is based on iterative demapping and decoding, wherein the demapper delivers soft information to the decoder and accepts feedback from the decoder.
Still further, in WO 02/061952 A1 there is described a turbo encoder with transmitter diversity employing space-time spreading transmission to improve transmission error performance and efficiency in addressing multi-path fading.